Experimental Vaccine to Treat Breast, Ovarian Cancer Shows Promise

Dispatching cancer cells with the same precision that vaccines dismiss bacteria and viruses may soon be possible, according to scientists at the National Cancer Institute who are working on an experimental vaccine that helps the immune system target breast and ovarian cancer cells.

The difference is that the shot would treat, rather than prevent, cancer. Dr. James Gulley and his colleagues report on the strategy — called immunotherapy — in the journal Clinical Cancer Research.

The study involved 26 women in advanced stages of breast or ovarian cancer; most had already had several rounds of chemotherapy as well as surgery or radiation therapy. They were all inoculated with a vaccine containing proteins commonly found on breast and ovarian tumors, along with other components designed to stimulate the body’s immune system to recognize cancer cells more readily. The combination proved to be promising — among the 12 breast cancer patients, the median time before they saw any progression of their disease was 2.5 months, and the median survival was over one year. For the women with ovarian cancer, the overall survival was slightly longer, at 15 months.

As intriguing as the results are, the trial did not involve a control group of women at similar stages of disease who were not treated with the vaccine, so Gulley could not determine if the vaccine actually provided any benefit, but he says the study is an important first step in justifying such a controlled trial. One woman with breast cancer who had already undergone a lumpectomy, radiation, chemotherapy and a hysterectomy that included removal of her ovaries showed a complete response to the vaccine; after three years, tumors that had spread to her lymph nodes had regressed. “We don’t need a control group to say [these results] are a good thing,” says Gulley. “We don’t see this in breast cancer. We don’t see tumors spontaneously going away.”

That doesn’t mean that women can expect to get vaccinated against breast or ovarian cancers any time soon. The study was a small one, and the absence of a control group made it impossible to determine whether the vaccine extended patients’ lives compared to current treatments. But the fact that patients showed some response suggests activating the body’s immune responses might be another way to fight cancer. The theory, says Gulley, is to awaken the immune defenses with triggers from the vaccine; from there, the body should be able to mount a stronger and broader response targeted specifically against the growing tumors, in a sort of cascade effect.

The antigens Gulley’s group selected to include in the vaccine have worked, separately, in animal studies to target and mark cancer cells for destruction. But they haven’t been studied together, and they haven’t been combined in a vaccine that also included immune system stimulators to boost their effect. The animal studies have showed that targeting multiple parts of tumors in this way results in better outcomes. The current trial shows that may be possible in cancer patients as well.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny . You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.